1. Field of the Invention
The present invention relates to an image forming apparatus and a radiation detection system, and particularly to an image forming apparatus including a liquid crystal panel and a photoelectric conversion apparatus, and a radiation detection apparatus and a radiation detection system for detecting radiation containing X-ray, α-ray, β-ray, and γ-ray.
2. Related Background Art
In recent years, rapid progresses are being made in increasing the size of a panel using a TFT and increasing the drive speed. Those circumstances have been affected by the development in techniques for manufacturing a liquid crystal panel using a TFT and by the application of an X-ray image pickup apparatus having a photoelectric conversion element and the like to each field of area sensors.
Also, concurrently with the increase in panel size, progresses in finer pixel pitches and finer wiring widths have caused a tendency to increase the wiring resistance of each unit. In a liquid crystal panel, the finer pixel pitches cause reduction in the pixel aperture ratio, thereby reducing the amount of light from a backlight. Thus, it is difficult to provide a liquid crystal panel having a high brightness.
Also, the increases in panel size have caused increases in wiring pattern length, and the finer wiring patterns have caused increases in wiring resistance, thereby increasing the time constant and reducing the drive speed for a TFT.
Similarly, in the X-ray image pickup apparatus, the reduction in the pixel aperture ratio causes reduction in the area of a sensor light receiving unit, thereby reducing the sensitivity of a sensor. Also, if the drive speed of a TFT is reduced, there is a case where the sensor cannot be used as a dynamic image sensor, thereby limiting the application of the sensor.
FIG. 8 shows an equivalent circuit for a matrix panel using a conventional TFT. Here, an example will be described of the matrix panel applied to a photoelectric conversion apparatus or a radiation detection apparatus.
Each pixel shown in FIG. 8 is composed of a pair of a thin film transistor unit (TFT unit) 12 and a photoelectric conversion element unit 11.
The photoelectric conversion element unit 11 generates electrons and holes when absorbing light, and accumulates the electrons or the holes in a capacitor that is provided to the inside thereof.
Then, by driving a gate driver circuit unit 17, an on voltage for turning on the TFT unit 12 is applied to gate lines 13 to drive the TFT units 12. Thus, the electrons or the holes accumulated in the capacitor are transferred directly or indirectly through the TFT units 12 from data lines 14 to a signal processing circuit unit 15 to display an image.
At this time, in the case of the photoelectric conversion element unit 11 of a metal-insulator-semiconductor (MIS) type, an operation is necessary of applying a forward bias from a common electrode driver circuit unit 16 to a common electrode wiring 10 to remove the electrons or the holes accumulated in an insulating film interface.
Alternatively, if a phosphor layer for converting radiation into visible light is arranged on an upper portion of the matrix panel, or if amorphous selenium, lead iodide, or mercury iodide which generates electrons and holes directly from radiation is used as a photoelectric conversion element, a radiation detection apparatus can be obtained.
For a liquid crystal panel, the photoelectric conversion element unit 11 is replaced by a liquid crystal capacitor unit 18.
The example described above presents the following problem.
That is, a demand on the photoelectric conversion apparatus or the like when the TFT unit 12 is driven at a high speed is different from a demand thereon when the TFT unit 12 is driven at a slow speed, and it is difficult to meet the two demands simultaneously.
When driven at a high speed, the speed of response is given a higher priority. That is, it is a higher priority to remove artifacts with respect to a display/take-in image due to an after-image in both the liquid crystal display panel and the photoelectric conversion element panel which is generated when the speed of response is reduced.
On the other hand, when the TFT unit 12 is driven at a slow speed, a higher priority is given to displaying or taking in of an image having a high definition and a high contrast than the speed of response.
Up to now, in order to execute individual photography, it is publicly known to use films having various resolutions, for example, a combination of films/sheets or storage sheets. An example using them is an X-ray image amplifier having a low lateral resolution and a magnification power that can be switched over for the purpose of transmission irradiation. Also, an X-ray diagnostic apparatus for performing a selection operation between a high-frame mode and a high-definition mode is publicly known.